Cardiac arrhythmias, such as atrial fibrillation, are irregularities in the normal beating pattern of the heart and can originate in either the atria or the ventricles. Atrial fibrillation is characterized by rapid randomized contractions of the atrial myocardium, causing an irregular, often-rapid ventricular rate, and can give rise to other forms of cardiovascular disease, including congestive heart failure, rheumatic heart disease, coronary artery disease, left ventricular hypertrophy, cardiomyopathy or hypertension.
Treatments for atrial fibrillation have focused on the pulmonary veins, which have been identified as one of the origins of errant electrical signals responsible for activating atrial fibrillation. In one known approach, tissue is ablated in a circumferential pattern at locations such as the within the pulmonary veins, at the ostia of the pulmonary veins, or surrounding the pulmonary veins. By ablating the heart tissue at these locations, the electrical conductivity from one segment to another can be blocked such that the resulting segments become too small to sustain the fibrillatory process on their own.
In order to reach locations within or surrounding the heart, guide catheters are commonly used. Most guide catheters have proximal and distal ends connected by a long, tubular body having one or more lumens formed therein. The proximal end of the catheter usually includes a handle for control of the catheter by the operator and various ports for introduction of fluids and instruments through the catheter lumen, and the distal end includes a tip which is inserted into the patient. For example, in vascular applications, the tip of the catheter can be inserted into a major vein, artery, or other body cavity. The catheter is then further inserted and guided to the area of concern. Moreover, the catheter can also function as a “sheath” or “guide catheter” in that it can be used a delivery conduit for other tools, such as balloons and/or stents for performing angioplasty or other instruments mapping electrodes and ablation devices for conducting procedures within the heart.
Current methods for inserting and guiding a catheter include the use of a guide wire where the guide wire is fed into position within the patient and then the catheter is passed over the guide wire. However, one drawback associated with this method, when the target ablation sites are in or near the pulmonary veins on the posterior surface of the heart, is that it is often difficult, if not impossible, to advance the guide wire all the way to the ultimate target site due to the shape of the heart muscle.
Alternatively, a steerable catheter can be used. Steerable catheters require an ability to selectively deflect the distal tip of the catheter in a desired direction by permitting an operator to adjust the direction of advancement of the distal end of the catheter, as well as to position the distal portion of the catheter. The deflection of the distal tip is typically provided by one or more pull wires that are attached at the distal end of the catheter and extend to a control handle such that the surgeon can selectively deflect the tip and/or rotate the catheter shaft to navigate into the correct position.
When designing such steerable catheters for access into the heart, it is important to have sufficient flexibility in the catheter shaft so that when the catheter is advanced through a blood vessel or heart chamber it can follow the inherent curvature of the biological structures without puncturing them. However, achieving a balance between the “pushability” of the catheter (that is, the ability to direct the tip of the catheter to the target location without buckling or kinking) and the necessary stiffness to allow the catheter to access the heart, especially when navigating the sharp turns necessary to access locations in the left atrium of the heart, can be difficult.
Prior art deflectable catheters typically have a single stiffness value, or at best, one stiffness value for the catheter body and one stiffness value for the deflectable tip. As a result, these catheters often require large spatial volumes in which to bend and are unable to make tight turns that are sometimes necessary to reach a target region without causing trauma to a patient. Particularly, access to the left atrium for the treatment of atrial fibrillation is particularly difficult when the ultimate target region is in the vicinity of the right inferior pulmonary vein, as this vein is usually the closest to the transeptal puncture, requiring the catheter to turn 180° in direction in order to achieve proper orientation.
Currently methods to address this issue include using a set of sheath catheters with different curves and removing one catheter and replacing it with another, several times. However, this exchange is time consuming and can present additional risks, such as accidental entrainment of air embolisms.
More difficulties arise when the catheter includes an ablation instrument having a balloon, as additional maneuvering can be required to properly orient the balloon within or at the mouth of the vein. Further, axial force may be required in order to occlude the pulmonary vein at the ostium and the lack of stiffness of most catheters renders the application of sufficient force to successfully seal the vein prior to ablation problematic.
Accordingly, there exists a need for deflectable sheath catheters that can navigate and access narrow and limited spaces leading into, and within the heart, especially the left atrium. There also exists a need for improved methods of treating atrial fibrillation that provide better and/or more precise location of ablation instruments within the heart.